This invention generally relates to semiconductor processing methods including formation of tungsten metallization plugs and a method to salvage the process wafer by reworking tungsten particle contaminated process wafers.
Metallization interconnects are critical to the proper electronic function of semiconductor devices. Several advances in semiconductor processing have been aimed at improving signal transport speed by reducing metal interconnect resistivities and improving resistance to electromigration effects. Copper has increasingly become a metal of choice in, for example, upper levels of metallization in a multi-level semiconductor device due to its low resistivity and higher resistance to electromigration. Tungsten is still preferred for use in the lower metallization layers adjacent to the silicon substrate since it provides an effective diffusion barrier to metal diffusion from overlying metallization layers to react with the silicon substrate. Tungsten further has high resistance to electromigration and can effectively be used to fill high aspect ratio vias by chemical vapor deposition (CVD) processes.
For example, referring to FIG. 1A, a cross sectional side view of a portion of a semiconductor wafer is shown having a first metal layer 12, formed of, for example, an aluminum:copper alloy. A barrier/adhesion layer 14, for example titanium nitride, is provided over the metal layer 12. Overlying the barrier/adhesion layer 14 is formed an electrically insulating interlayer dielectric (ILD) layer 16, also referred to an intermetal dielectric (IMD). The IMD layer 16 is formed from silicon dioxide which is frequently doped with fluorine or carbon to lower the dielectric constant thereby decreasing signal slowing parasitic capacitances. Another barrier/adhesion layer (not shown), also functioning as an anti-reflective coating (ARC) to reduce undesired light reflections, for example titanium nitride, is optionally deposited over the IMD layer 16 prior to a photolithographic patterning process to form a via etching pattern.
Still Referring to FIG. 1A, a via opening 20 is anisotropically etched through the IMD layer according to a reaction ion etching (RIE) process to form closed communication with the underlying metal layer 12. A barrier/adhesion layer 18, for example, titanium nitride is then blanket deposited over the via opening to form a barrier/adhesion layer lining the via opening 20.
Referring to FIG. 1B, tungsten is blanket deposited by a CVD process to fill the via opening 20 and form an overlying tungsten layer 22 over the barrier diffusion layer 18. Referring to FIG. 1C, the excess tungsten metal overlying the barrier diffusion layer 18 above the via level is then removed according to a tungsten metal dry etching (plasma etching) etchback process.
A serious problem with the prior art method of using a dry etchback process to remove the tungsten metal above the via level is that during the dry etchback process unetched residual tungsten particles or areas e.g., 22A, 22B ranging in size from about 0.5 microns to about 40 microns of particles frequently remain on the wafer process surface. It is believed that the unetched tungsten areas are caused by tungsten particles forming on the surface thereby acting as etching masks, preventing the etching of underlying tungsten. Tungsten particle formation is a serious problem in both CVD and etching. The tungsten metal does not adhere well to most surfaces including heated surfaces. In addition, stresses build up quickly in deposited tungsten, for example on the wafer backside or chamber walls ultimately causing flaking off of tungsten particles. The problem is exacerbated in a subsequent dry etching process making it necessary to clean the wafer edged and backside portions of tungsten including time-intensive and frequent cleaning of the etching and deposition chambers.
The unetched tungsten areas resulting from tungsten particle contamination on the wafer process surface make further dry etching impractical as the underlying barrier/adhesion layer and the IMD layer will be partially etched away in the process affecting wafer surface planarity and wafer design constraints. Wet etching or cleaning processes are also costly and impractical for removing the tungsten residue. According to prior art practices, the tungsten residue on the process wafer surface frequently makes scrapping (disposing of) the process wafer the only viable economic alternative.
Therefore, there is a need in the semiconductor processing art to develop a method for reworking a semiconductor process wafer following tungsten etchback to remove overlying residual unetched tungsten areas or particles while minimizing process steps and preserving the underlying material process layers.
It is therefore an object of the invention to provide a method for reworking a semiconductor process wafer following tungsten etchback to remove overlying residual unetched tungsten areas or particles while minimizing process steps and preserving the underlying material process layers while overcoming other shortcomings of the prior art.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention, as embodied and broadly described herein, the present invention provides a method for reworking a metal particulate contaminated semiconductor wafer process surface following a metal dry etchback process.
In a first embodiment, the method includes providing a semiconductor wafer including a dielectric insulating layer having anisotropically etched openings lined with a first barrier/adhesion layer formed according to a blanket deposition process and an overlying metal layer formed according to a blanket deposition process filling the anisotropically etched openings; dry etching in an etchback process to remove the metal layer to form a process surface revealing at least a portion of the first barrier/adhesion layer; performing a chemical mechanical polishing (CMP) process to rework the process surface to remove a remaining portion of the metal layer including the first barrier/adhesion layer to endpoint detection of the dielectric insulating layer; and, blanket depositing a second barrier/adhesion layer over the dielectric insulating layer.
These and other embodiments, aspects and features of the invention will be better understood from a detailed description of the preferred embodiments of the invention which are further described below in conjunction with the accompanying Figures.